1. Field Of The Invention
This invention relates to the field of single chip microprocessors and controllers. In particular, this invention relates to circuitry which brings certain internal signals of a controller to the user interface to allow a user to customize the controller for use with peripheral devices without the expertise of custom layout and device/circuit engineers.
2. Prior Art
Single chip microcontrollers having onboard functionality usually performed by peripheral controllers are well known devices. A representative controller sold by Intel Corporation having such onboard functionality is known as an 8051 microcontroller which incorporates a serial channel which provides input/output for serial devices. In the 8051 controller, a special function register (SFR) area is provided which is used by the software to "talk" to the outside world. Although not part of a standard 8051 controller, other frequently desired functionality includes analog-digital and digital-analog converters as well as various special purpose controllers. While it is possible in the prior art to provide such additional functionality by allocating one or more of the onboard ports as an address and data bus, since not all controller instructions can address the data and address bus normally used to interface with peripheral devices, additional programming is necessary which necessarily slows down input/output, requires additional memory space and generally results in poorer performance. For example, in an 8051 microcontroller, only 4 out of 76 instructions, and none of the bit manipulation instructions, can directly access a peripheral device controller attached to a port.